The invention concerns a process for manufacturing metal sections, in particular in aluminium alloys, continuously rolled by a series of pairs of rollers from an as-cast bar obtained by continuous casting in a grooved wheel, possibly followed by one or more stages of discontinuous or continuous wire drawing and annealing.
For many years wire rod has been manufactured in non-ferrous alloys, particularly in aluminium alloys, from an as-cast bar continuously cast in the groove of a wheel which is rotated, the groove being blanked off by a tape engaged by the wheel. Known casting systems are those with 2 wheels with a small support wheel, 3 wheel systems, like the Properzi casting described in GB patent 1143264, 4 wheel systems like the Pechiney 4R casting described in FR 1178580, and 5 wheel systems like the one described in US 3416596.
The as-cast bar, of generally triangular or trapezoidal cross-section, is then continuously rolled through a series of successive stands made up of two rollers, and alternately horizontal and vertical, so as to obtain a wire of circular cross-section, which may be used as such or transformed by drawing.
In the case of aluminium alloys the process is widely used for light alloys, intended particularly for electrical conductors. With some adaptations, described for example in the patents FR 2234936 (Secim and Pechiney Aluminium), FR 2304414 (Secim) and FR 2359613 (Pechiney Aluminium), it has been possible to cast and roll without causing porosities of more heavily alloyed alloys with a higher solidification range, such as alloys of the 2000, 5000 and 7000 series according to the designations of the Aluminum Association, which can be used for mechanical applications.
To the knowledge of the applicant company, none of the existing continuous casting-roll machines has ever manufactured products of non circular cross-section. To be sure, it is normal to use round wire rod when the drawn end product is itself a round wire, which is the case for example for electrical conductors or wire for netting. There are, however, particularly in mechanical applications, drawn products of non circular cross-section, for example rectangular, triangular, polygonal or T-shaped, for which it would be more economical to start from a wire rod of related shape, which would reduce drawing passes, or even to leave the casting-roll machine in the final size without subsequent drawing.
One of the reasons which might explain the absence on the market of wire rod of non circular cross-section stems from the difficulty of controlling the geometry of the section during rolling. For a circular cross-section in fact, the product emerging from the final rolling stand remains on the groove of the rollers only via a generator, and its separation at output poses no problem. It is not the same for products whose cross-section comprises a plane part, for example a rectangular, triangular or T-shaped cross-section. They remain on the groove of the rollers of the final stand in a more or less wide band, the uneven detachment of which entails distortions in the geometry of the rolled product, as well as surface defects.
The purpose of the invention is to overcome this drawback and to allow accurate control of the geometry of the cross-section of the rolled product, when this cross-section comprises a polygonal part, i.e. at least two straight secant parts. The rolled section can then be used directly as it is, either continuously or discontinuously drawn so as to obtain a wire of non circular cross-section, with a smaller number of passes than starting with a circular section.
An object of the invention is a process for manufacturing metal sections of partially or totally polygonal cross-section by continuous casting in a grooved wheel and continuous rolling by means of at least 3 and preferably 3 to 8 pairs of rollers fitted with a peripheral groove, these rollers being placed symmetrically relative to the section, and alternately horizontal and vertical, a process which is characterised in that:
the grooves of the first pairs of rollers are identical to those of the rollers used for the manufacture of sections of circular cross-section,
the final pair of rollers comprises grooves delimiting a cross-section approximately corresponding to that of the section desired,
the cross-section formed by the grooves of the final pair of rollers has at the apexes of the polygon radii of curvature between 1 and 5 mm,
the sides of the polygon non parallel to the gap of the final pair of rollers have, relative to the corresponding sides of the cross-section of the final section a clearance between xc2xd and 3xc2x0.
An object of the invention is also a process for manufacturing discontinuously or continuously drawn metal sections of partially or totally polygonal cross-section from as-cast bars of partially or totally polygonal cross-section obtained by continuous casting in a grooved wheel and continuous rolling, in which the number of discontinuous or continuous wire drawing passes and the number of annealings are each reduced by at least one third relative to the process of the prior art starting from an as-cast bar of approximately circular cross-section.